Exemplary embodiments of this invention generally relate to an air turbine starter and, more particularly, to a retention feature for retaining a planetary gear system in an air turbine starter.
Gas turbine engines, such as those used in aircrafts for example, require significant torque be applied to rotate a compressor, and thereby provide sufficient compression to start the engine. Electric motors powerful enough to provide such torque can be used, but are relatively heavy. In applications where gas turbine engines are used for transportation purposes, for example aircraft propulsion and power, the extra weight of an electric motor is undesirable. An air turbine starter (ATS) is generally employed as a substitute in such applications. The ATS is powered by compressed air from an external source. The compressed air passes over blades of an air turbine in the ATS and exits the ATS through an air exit port. As the air turbine rotates, it rotates a series of shafts connected to the compressor in the gas turbine engine, thereby providing sufficient torque to start the engine.
Conventional ATS systems include a planetary gear system. A sun gear rotates about a central axis, and a ring gear rotates outwardly of the sun gear. Multiple planet gears are positioned to transmit rotation between the sun and ring gears. In a known type of planetary gear system, the planet gears are mounted on stationary shafts such that each shaft provides an inner race for bearings which support the planet gears. In such applications, a significant force is continuously transmitted to the same angular portion of each planet shaft.